This invention relates to an apparatus for detecting the volatility of the fuel supplied to an internal combustion engine.
It is the current practice to minimize the emission from the engine of pollutants by employing less volatile fuel such as leadless high-octane fuel. With no proper conformity between the fuel volatility and the engine control characteristic, however, the engine cannot operate at a desired air/fuel ratio, resulting in degraded driveability and increased emission of pollutants. For example, as the fuel volatility decreases, the air/fuel ratio will be leaned particularly during engine starting operation due to an increased amount of fuel collected on the inner wall surface of the intake passage, and vice-versa when the fuel volatility increases. Therefore, the fuel volatility should be measured with high accuracy to ensure that the amount of fuel supplied to the engine is correct to maintain a desired optimum air/fuel ratio. For this purpose, an electrostatic capacity type fuel volatility detecting sensor has been used. However, such a sensor is very expensive.